OF ARTS AND SCIENCES. 79 



The analyses lead to the formula 



10 M0O3 . 2 PPs . 5 (NIIJ.p . 11,0 + 6 aq, 

 or 



5 M0O3 . T.fl. . 3 (NII,),0 + 5 M0O3 . PA • 2 (NllJaO . UrP + 6 aq, 

 which requires : — 



2110 100.00 



The phosphoric oxide was determined by double precipitation only, 

 without subsequent treatment with amnionic sulphide. The percent- 

 age is a little lower than that required by the formula, which is 

 unusual ; but the general agreement of the analyses with the formula 

 is satisfactory. Rammelsberg has described an acid potassium salt 

 with the formula 



10 M0O3 . Vfi. . 5 K,0 . Hp + 1 9 aq. 



It is therefore at least probable that we shall find another ammonia 

 salt with 20 atoms of water, and another potassium salt with 7 atoms. 

 Zenker has described another potassic salt to which he gives the 

 formula, — as I should write it, — 



9 M0O3 . P^O. . 4 K,0 . 2 H.O + 18 aq ; 



but the results of his analyses differ very widely from the percentages 

 required by the formula, and on repeating his process I obtained 

 only the 10:5 atom salt of Rammelsberg. The formula given above 

 for this salt requires 11.11 % P2O5. I found 11.22%. 



Rammelsberg* has also described a white insoluble potassium salt 

 to which he gives the formula 15 MoO, . P2O5 . 5 K2O, but without any 

 statement of his analyses. 



ARSENIO-MOLYBDATES. 



Compounds of arsenic and molybdic oxides have been described 

 by Seyberth f and by Debray.f Seyberth obtained an acid with the 

 formula, — as I should write it, — 



* Loc. cit. 



t Berichte der Chem. Gesellscliaft, 1874, p. 391. 



t Comptes Rendus, Ixxviii. 1408. 



